Disclaimer: I don't have engineering degree, don't have experience with working on cars, don't have much experience with cars period, so this is all based off theory and info that I read
EGR is primarily for emissions reduction since it both lowers burn temperature by decreasing oxygen concentration and allows the unburned hydrocarbons to pass through the engine a second time. It has the benefit of reducing throttling by a bit, but I think emissions compliance is the main reason it's there.
Lean burn at low specific output is a better strategy as the greater amount of oxygen and lower intake temperature help efficiency, but for effective "throttling" based purely on reducing the amount of fuel, the air to fuel ratio is going to be very high and efficiency will be hurt, but since everything is happening at lower temperature theoretically it's better than EGR.
Ideally you'd want to be able to limit intake volume/pressure losslessly, and then increase the compression ratio as much as possible dynamically to keep the gas cycle efficiency up. However in this scenario, you still have to fight friction so at the end of the day BSFC still increases at lower load.
Tesla, as for pulse and glide on flat roads, you definitely are increasing energy spent to travel each distance because your speed is wavering. The average speed is a harmonic mean in some sense, so if higher speeds consume anything more than proportionately (linearly) more power, then not keeping a constant speed will result in a net increase in energy dissipated by the car.
The problem is if you look up a BSFC chart and figure out the power you need to cruise on the highway at say 60mph, most cars are operating their engines at 70% or worse efficiency, so pulse and glide easily makes up for the apparent disadvantage in power requirement.